Mycoviruses were detected and studied in Helminthosporium maydis, Thielaviopsis basicola, and Saccharomyces cerevisiae. All apeared to be multicomponent in nature and had genomes consisting of double-stranded RNA. Complete biophysical description of these ds-RNA viruses will be made. Methods of transmission of ds-RNA viruses of mycovirus origin are under study. The use of ds-RNA of mycovirus origin as inducers of interferon is under study.